It's Conway's Game of Life, but it runs on Google Spreadsheets! It's a bit slow, but it works.
- Create a new spreadsheet in Google Spreadsheets.
- Go to Tools -> Scripts -> Script Editor
- Paste game-of-life.js into the window and hit save.
- Reload the spreadsheet!
You should at this point have a new menu "Game of Life." If you choose, "Random Board," you'll get a random start position. Choose "Gosper Gun" to get a known interesting start state. Then choose "Next Generation" to compute the next generation of the simulation.